Blood Test Primer

When it comes to thyroid health, one of the most confusing and frustrating topics seems to be the interpretation of blood tests. What tests should I get? What do the results mean? What do I do if the test comes back in the normal range, but I don’t feel “normal”? How do I get the doctor to give me a new test?

Let’s start with a listing of the various thyroid tests that are available and what the results could mean. Please remember, this is just a starting point and accessing test results is more than just determining if the levels are within the established normal ranges. As always, I advocate for listening to your body and digging further is something doesn’t feel right – you know your body better than anyone.

During my research of thyroid blood tests, I found inconsistencies in what are considered the “normal” ranges. Therefore, I will list multiple ranges for a particular test where indicated.

Thyroid Stimulating Hormone (TSH)
Normal Ranges
.35 – 5.50 mcIU/ml
.30 – 3.0 mcIU/ml*
.35 – 2.1 mcIU/ml**
Below range indicates hyperthyroidism. Above range indicates hypothyroidism.

Serum Thyroxine (T4)
Normal Range
4.5 – 12.0 ug/dL
Below range indicates hypothyroidism. Above range indicates hyperthyroidism.

Tyroxine Free, Direct (FT4)
Normal Ranges
0.7 – 2.0 ng/dL
0.7 – 1.53 ng/dL**
Below range indicates hypothyroidism. Above range indicates hyperthyroidism.

Serum Tri-Iodothyronine (T3)
Normal Ranges
80 – 180 ng/dL
85 – 205 ng/dL**
Below range indicates hypothyroidism. Above range indicates hyperthyroidism.

Free Tri-Iodothyronine (FT3)
Normal Ranges
2.3 – 6.19 mg/mL
2.3 – 4.2 mg/mL**
Below range indicates hypothyroidism. Above range indicates hyperthyroidism.

Reverse T3 (rT3)
This test evaluates thyroid function and metabolism. It may be an indication of clinical situations other than/or in addition to thyroid imbalance.

Radioactive iodine update or T3 Uptake
Normal Ranges
10 – 30%
24 – 39%**
Below range indicates hypothyroidism. Above range indicates hyperthyroidism. Test results above or below the normal range can be an indication of a thyroid nodule.

Thyroid Antithyroglobulin Antibodies, Thyroglobulin (AgAb or ATA)***
Normal Range
<115 IU/mL
Any reading above the normal ranges can be an indication of Hashimoto’s thyroiditis.

Thyroperoxidase Antibodies, Thyroid Peroxidase (TPOAb or TPO)***
Normal Range
<35 IU/mL
Any reading above the normal range can be an indication of Hashimoto’s thyroiditis.

Thyroid Stimulating Immunoglobulins (TSI)
Normal Range
<1.3
Any reading above the normal range can be an indication of Grave’s disease.

*Range revised by the American Association of Clinical Endocrinologists 2003.
**Life Extension Optimal Range.
***Some doctors believe the presence of any thyroid antibodies is an indication of Hashimoto’s thyroiditis and should be addressed before allowing the disease to progress.

Please use this information as a starting point to help evaluate your blood tests. It is very important that you ask for copies of your lab results and keep track of your tests over time.